Method of reducing corrosion and plugging of solvent extraction process equipment



METHOD OF REDUCING CORROSION AND PLUGGING OF SOLVENT EXTRACTION PROCESS EQUIPMENT Filed Sept. '7, 1955 Aug- 5, 1958. LE ROY w. HOLM mL 2,846,354

- Aleus in the csideilsing phenolic.

`METHOD F REDUCINGCORROSSION ANDPLUG- *SLVENT 'EXTR'ACTION PROCESS l EQUIPMENT I v This-invention relates to amethodyfor increasing the eiciency of` solventvextraction processes utilized vin the remng of .oils yandy-more particularly, to a method for mitigatingcorrosion during the phenol 'extraction of mineral `lubricating oils. Solvent extractionhas for sometimelbeen used to supplement theconventional treatments of y lubricatingoils, such as distillation and/or: clay treating. In United States Patent 2,673,174 ,P. King, a process of solvent ,extraction is described based on the finding that the presence o f certain smallwamountswof ammonial eifectively enhance the phase separation and increase theyield of high l viscosity index rainate oilI ,o btained. AIn accordance with United States Patent 2,701,783 by Long and B asch,

litis disclosed that presence of between about 0.2

*99:4 volume pjementpfammnia based 011 the amount of vfeed oil in Ythelextrgaton zonehas the effect of aiding in the recoveryvof ratnates` havinga relatively low neu-A tralization number.

"'1 states 'Ptent 2,128,029 has utilized `substantial amounts of anhydrous ammonia as a means forv recoveringthe selective solvents of `the phenolr type. 'T The reeoyery is accomplished by reactinggthe phenolic s olven't'withtm aminoniatofform a compound which ek; 'denn #weer ,the amper coditions' to ecovered phenolic-type solvent and ammonia fc'orlingly,Y is i'irelate d tqthepresentprocess. It has beeny discoyefed hat theoperation ofthe K ing prpc'ess`f( sp a)- e h ot phenolpassing from the :extret ilash-t'wercarrieswith it certain corrosive, acidic,

oxy-coinpounds to be described), which cause severe corrcsion in the reboilers and heat exchangers associated iyit'lith l transfer linefcarrying the recovered phenolic v`sblx'feit to storage. I t has also beendiscoveredthat these acidic materialsl reet -with the vmetals in thetransfer line and attendant-'equipment to form insoluble materials ess does ,I-mployehlextract flash-tower and, ac-

materials are formed during the highteni'per iir'efsre tion of phenols from the phenolicsolvent and the corrosive environmentis at va maxnnum at these vbyineansr of line 26.

Fice

points inthe system.

Accordingly, it Vvis'an vobject of this iriventi'nt a method Vof solvent refining which "obvitesforfnnt s the corrosion in the :phenolic solvent a solvent rening process.

Itis a further object of lthis invention tbvite mitigate corrosion without causing or contributmgto the i form ation of 'equipment-plugging, l solid precipitates The accompanying drawing isa- How diagram of ventional phenol extraction lprocesswith which the( preheated petroleum oil charge stock, which' may `c s t of a low, intermediate, 4or high viscosity lub" eating vjil stock obtained as a side-stream from thevacuumdist'illation of a toppedy crude, or from the deasphaltedreidinvention may be used. Referring'tothe drawing the uum produced in the vacuum distillationproce'rss, is introduced by means of ,line 10 into phenol absorber-tower l1 wherein it is c'ountercurrently contacted with constant-boiling mixture of phenol `and water obtained -fr'orn a hereinafter-mentioned source. This initial tretner'it eiiects the removal ofthe phen'ol from the eonstantibiling mixture and eliminates the necessity for `ernployin'gl'a distillation process for separatingjthe constituents of, phenol-water mixture, the separation of Whichfwuldbfe extremelydiflcult because of the Icloseness iofthe.,boiling points of the `distillate fand the mixture from which the distillate is being produced. 'L

The process water is Aremoved 4inthe v:valOfOus'state fromabsorber tower 1 1 byline 1 2 which transfers the `phenol-free vwaterto the waste disposalgjsystem o f. the' renery. The charge. st ock,j, containing minor: amountsv of phenol removed from the phenolicwatelr', is thenpasse'd by line 1 3 to extraction t ower 14 wheregitis countercurrently eontactedyithphenol toextract the undesirable constituents from the lubricating-.oily basetockLQ, The

phenol employed this operationl isintroduced into, the

rop of extraction tower 1 4 bymeans ot v111116.15..which connects the extraction` tower with phenolstorage facility 1 6. A'dditional watertdaidphaseseparationfis added throug'lilin'e 117.v Because of'theipimmiscibilityf, thetwo liquids contacted in extraetion, towerv H Separatejinto two. phases, namely, an'oilLrich *or ratiinatephase which is withdrawn from 'the op ff means of vline 18, and A,a solvent-rich orge which'isV withdrawnV from the bottom ofthe treating 'tower lfhe verhead villir'ia'te prodiiet is' transfert-ted o traction tower 14 kby means o f line" 1 8 totheeyaporator or flash section' Z1 `of raiinate tower. 19. j While ,being transferred, it passes through raiinate furnace `20 wh er e` which, upon leatiiigz in.v the exchangers, precipita te `and in it is heated to an elevated yte'rnperature suflicie tto et- .fect the flash distillation of fhe'phdl const itentprtlie raffinate phase'in asli section 21. Ilesubstaiitially anhydrous phenol produced is transferred. v1 i to storage tank 16.v The ranate solution containing y minor amounts of phenol passes into theustr ping section 23 v'of rainate tower- 19 by meansofzlinewg I n this s ection, the ralinate .is denuded of traee amounts of remainingphenol by meansl osteam stripping The finished raffinate, haying distinctly improved c h teristics of viscosity index, earbon' residue,' and general stability, passes from `line 25 to subsequent processing 27 `and is introduced at an elevated tempcra'tureto'extt i 2,846,3545 Patenten: e?! i recovery "system of drier' 28 wherein the water contained therein is separated. There is also eiected a partial phenol separation in this step, and as a result, the water and phenol are removed by line 29 asa vaporous, constant-boiling mixture of phenol and Water. The elevated temperature required for this dehydration may be obtained by passing the extract solution in indirect heat exchange with other process streams or other-suitable means. The anhydrous extract, still containing as much as 80% of phenol, is then Withdrawn from the bottom of drier 28 and transferred via line 30 to extract {lash-tower 31 wherein most of the phenol is separated by ash distillation. This phenol is normally removed as overhead euent at line 32, passed directly through reboiler 33 and returned tothe phenol storage 16 via lines 34 and 35 by way of coil 36 in heat exchanger 27. Reboiler 33 supplies Vthe heat necessary. to operate drier 28. Similarly, extract furnace 37 supplies the heat to extract ilashtower 31 to insure the substantial removal of most of the phenol from the anhydrous extract circulated therethrough by means oflines 38 and 39.

The bottoms from the flash tower 31 are then fed by line 40 into extract stripper 41. In this vessel, the remaining traces of phenol contained in the anhydrous extract are eliminated by means of steam stripping. The extract oil is removed from the bottom of stripper 41 by means of line 42. Although this extract oil contains the undesirable constituents separated from the lubricating oil base stock, it is nevertheless a marketable product which may be blended with fuel oils or used as a compounding agent in other types of compositions.

Phenol solvent initially introduced into tower 14 by means of line 15 is carried to the recovery section'of the process by the raiinate and extract streams. The separation and recovery of phenol from these respective streams is eifected in ranate tower 19, extract drier 28, and extract flash-tower 31 and returned through lines 22, 34, 'and 35 to storage. The remaining amounts of phenol are recovered from the system in the form of mixtures of phenol and water originating from a number of locations, that is, extract drier 28, the stripping section of rainate tower 19, and extract stripper 41. Phenolic vapors, comprising about 90% phenol and 10% water recovered from the stripping section of rainate tower 19, and extract stripper 41, are condensed and transferred to phenolic Water accumulator 43 by means of lines 44 and 45 respectively. Phenolic water vapor from drier 28, comprising about 90% water-and 10% phenol, passes via line 29 and branch line 46 into phenolic Water accumulator 47 Where it is condensed and collected.

Redux in the form of phenolic water is withdrawn from phenolic water accumulator 47 and returned to extract drier 28 by means of line 48. Phenolic water vapors not required for refluxing are transferred by lines 29 and 49, or by means of line 50, Vthrough steam ejector 51 and lines 52 and 49, to the phenol absorber-tower 11 wherein the phenol constituent in the phenolic water mixture is separated by contact with the preheated charge stock introduced into the tower as hereinbefore mentioned. Portions of the phenolic water from accumulator 43 are introduced into feed line 13 by means o'f line 53 or from accumulator 47, into tower 14 through line 54. The phenolic water is introduced to increase the internal refluxing and to raise the immiscibility temperature of the phenol, with the oil charge stock Within tower 14. Since the phenolic water changes the solvent characteristics of the phenol, the amount of phenolic water introduced into the extraction tower must be properly balanced to provide maximum eciency.

In accordance 'with the King patent (2,673,174), ammonia supply is maintained for addition to the phenol and the phenolic water stream to improve the operation of the process and bring about better tower extraction fcciency For this purpose, ammonia is injected into lines 44 and 45 going to phenolic water accumulator 43; into line 22 going to phenol storage; and into line 26 going to the extract' drier 28. We have found that even with the injection of ammonia into various parts of the system, there is severe corrosion in phenol returnline 32 passing to reboiler 33, and in line 34 and coil 36 within heat exchanger 27.

Therefore, in accordance with this invention, means are provided to treat this returning hot phenol stream with an oxide, hydroxide, or carbonate salt of calcium or barium. The oxide, hydroxider or carbonate salt of calcium is much preferred. The compounds of calcium mentioned are unique for the purposes of this invention in that their reaction products with components in the system have been found to be suciently soluble 1n said environment to preclude plugging the equipment. The compounds of barium are passable in this respect, but the compounds of magnesium, strontium, alummum, iron, sodium, potassium, and lithium are not suitable because the solubility of their reaction products in the phenolic environment is too low and plugging results. In view of this, it was entirely unexpected to nd that the compounds of calcium, and to a'lesser degree those of barium, were highly satisfactory and produced no plugging under normal circumstances.

Contact of the hot phenol stream returning to storage with the calcium or barium compounds of this invention may be accomplished in a number of ways. The phenol may be caused to pass through a statlonary bed of the calcium or barium compounds. An Injector system may be used whereby small amounts of the solid, comminuted compounds are picked up by the phenol as it'leaves flash tower 31 or at spaced points along the lines 32 and 34, preferably at points just before reboiler 33, as at line 55 leading into line 32, and just before heatexchanger 27, as at line 56 leading into line 34. i

A preferred system of contact of the calclum or barium compounds with the hot phenol stream is shown in the drawing. Returning hot phenol is diverted from line 32 into line 57 leading either to treater 58 or 59, or both, which are filled with vgranular solid particles of the calcium or barium compounds. Lumps, or beads of one or more of these'treating materials may be used. It is only necessary that a portion of the returning hot phenol contact the treating materials, since the effect thereof builds up within the system to control the corrosion. Two treaters, 58 and 59, are shown in order that the treating material within one may be replaced while the other is on stream. Treated phenol leaves treaters 58 and 59 by line 60 which connects again with line 32 passing to reboiler 33.

Depending somewhat upon the conditions existing within phenol return lines 32 and 34, the pretreatment of the phenol in treaters 58 and 59 or by injection of finely divided compounds at'line 55 will accomplishthe reduction of corrosion in the entire system. However, in order to insure that heat exchanger 27 is protected, additional treaters 61 and 62are placed in line 34 of the system and portions or all of the hot phenol passing through line 34 may pass through either or both of these latter treaters by means of lines 63 and 64.

The method of corrosion inhibition of this invention may be used along with the ammonia injection system of the King Patent 2,673,174, or may be used without such ammonia injection. It has been found that ammonia injection alone does not Vovercome corrosion in all parts of the system as experienced in the rerpound in each treater.

was analyzed and founclto .contain about40 lbs. perday of chloride, 700 lbs. per day ofvolatile organic acids representing about 0.04 weightlpercent'- of volatileor# ganic acids, and 50 lbs. per `day vofsulfu'r present as hydrogen sulfide. By periodic analysisfof equipment deposits present primarily in reboiler 33 and the coil 36 of'heat exchanger ,27,l it was found that in the normal corrosion process these" chlorides, organic acids and 'sulfur's are converted into iron salts. These analyses also disclosed that the sulfur cornpc'aundsl were apparently primarily vresponsible for equipment plugging. To ove'rcome this ,corrosion and plugging, aseries of tests was conducted todeter/mine which metals, more reactive than iron, formed sulfur compounds whichwere'more soluble in phenol than thek corresponding compoundsof iron. It was found thatr the calcium and barium salts of'these acidic materials were'the only reactive products which were satisfactory. In the case of sulfate salts, for example, it was found that calcium sulfate, `barium sulfate, magnesium sulfate and iron sulfate were the most soluble in phenol. Calcium sulfate was found to be soluble toY the extent of 0.014 weight percent, and barium sulfate tothe extent of 0.008 weight percent, while 'magnesium sulfate and iron sulfate were soluble only to about 0.004 weight percent in the phenol. Sulfate Vsalts of other metals, such as sodium, potassium and aluminum, were foundto be even less soluble vthan iron or magnesium. ltr/was -found that by treating the-extract ash-tower overhead streaml in line 32 with calcium oxide, the acid number of this phenol stream containing about 0.04 weight percent lof volatile acids and 6 p. p. m. of chloride `was reduced to zero..l Similarresults are obtainable using calcium hydroxide, calcium carbonate, or mixtures thereof.

By treatment in accordance with the example, it will Abe found that the corrosion and plugging Within those portions of the equipment in which there is condensing phenol will be greatly reduced. Also, there will be no plugging or corrosion in the conduits carrying the hot phenol overhead stream. Corrosion and plugging within such equipment as the reboiler 33 and the coil 36 of heat exchanger 27 will be negligible or substantially reduced. When using stationary beds of the calcium treating agent, such as may be contained in treaters 58 and 59 or 61 and 62, the hot phenolstream passing through line 60 into line 32 or through line 64 into line 34 will be non-corrosivel and free of plugging tendencies because the calcium salts formed in the treaters are soluble in the phenol. As an alternative, the hot phenol stream may be caused to pick up a small amount of the calcium compounds found to be effective through injection at points in the returning overhead phenol line just prior to apparatus in which condensation of the phenol will take place. This is illustrated by injection of the calcium compounds through branch lines 55 and 56. To accomplish this injection a venturi system may be used to incorporate the solid comminuted calcium compounds in the phenol stream or through the injection of a slurry ofl additional phenol carrying the calcium compounds and acting as a solvent therefor.

The amounts of calcium and barium compounds used to accomplish the results of this invention are not excessive. In most instances it will be found that reduction in corrosion `,and plugging can be obtained by maintaining an average of about 0.01 to 0.05 weight percent of the compounds based on the amount of phenol in the system. This concentration can be maintained by injecting about 20 to 25 lbs. per day of the calcium compounds. Where a stationary bed of the agent is used, it will be necessary to maintain from about 50 to 100 lbs. of treating com- Since the phenol stream entering treaters 58, 59, 61 and 62 is in vapor form, the main reaction of the treating agents with thev deleterious corrosive acids, chlorides and sulfur compounds takes place within the treaters. These reaction products are nonvolatile and are thus removed from the system. Only so faras some liquid phenol maybe equilibrium 'with the vapor streamer formed in the vtreaters will there be any carry-over of treating'agent 4into the'phenol stream leay-y ingI the treaters. Since the treating agents andftheirre'-v action products are soluble in liquid phenol, srnall qunf tities of both maybe carried along with the phenoll stream. This has two distinct advantages'.` It is aself-cleaning operation `for the treaters land yincreases the active contactr area of treating agent. The reactionproducts of treating agent arddleteriou's materials carried over even-y tually end up in the jextract oil phasewhich'is discharged. Secondly, anyy treating agent carriedv over isv presentv to inhibit corrosion-at, phenol-conderisingy pointsf'remo'ved from the treaters, asv in= the `frebioilerff33 and.` coil 36.; Re.- action products of this secondary inhibition reaction lalso end up in thev extract oil phas e. Becausel the 'treating agents are inexpensive 'and regeneration is uneconomical, any excess left in lone' treater after it has beenon* stream is ,discarded and replenished with afjnew supply.;v l

. Itis possible Ito treat the phenolri storagey or fresh phenol entering the ksystem with the..v treating Iagents of Y.

remain in kthe liquid phenolextractlphase passingthrough line'30' to extract ashftower 131' and: also find itsy way to thev extractoilphase, The 'Yphenolvapors from extract Hash-tower 31 would benufree of deleterious corrosive materials Vand accomplish the Vdesiredresults. However, it would be necessary to carefully control the amount of treating agent added in this manner so as to prevent overloading the extraction tower 14 and prevent carry-over of reaction products into the rainate phase.

Experience with the solvent extraction system has shown that the rate of corrosion in the returning phenol line is a function of the pressure and temperature. At any temperature above about 200 F; corrosion in the severest form has been found at those places in the system, as in Ieboiler 33 and coil 36 of heat exchanger 27, where the phenol is at the condensing point. Under atmospheric pressure this temperature of greatest corrosion will be about 356 F. Severe corrosion is experienced in the range of about 350 to 400 F. under which conditions the phenol may` be partially condensingor entirely in the vapor form. Accordingly, the invention is applicable broadly to reduction of corrosion by phenol at temperatures above 200 F. or between about 350 to 400 F. The invention finds particular application to the reduction of corrosion under those conditions where it is mos't severe, that is at the condensing point of phenol.

Although the invention has lbeen described by certain examples, the only limitations attaching thereto appear in the appended claims.

What is claimed is:

l. In a solvent refining process for improving the qualities of mineral lubricating oil wherein an oil is contacted with a phenol solvent to produce an oil-rich phase and a solvent-rich phase which lare subjected to heating conditions whereby the phenol solvent is' removed for recycle into the system, the improvement comprising main- 3. The method in accordance with claim 1 in which the material is calcium hydroxide.

4. The method in 4accordance with claim the material is calcium' carbonate.

5. The method in accordance with claim the material is barium oxide.

6.` The method in accordance with claim the material is barium hydroxide.

7. The method -in accordance with claim 1 'in which the phenol solvent contains a sutlcient amount of volatile organic acids, chloride and sulfur to cause corrosion in said process equipment.

8. The method in accordance with claim 1 in which the acid number of the phenol solvent is reduced to 4zero by said contact material.

9. The process for mitigating the corrosion of metal surfaces of process equipment in contact with phenol at elevated temperatures which comprises contacting said phenol prior to entry into said process equipment with a material selected fromV the group consisting of calcium oxide, calcium hydroxide, calciumy carbonate, barium 1 (in which 1' in which 1 in which oxide and barium hydroxide in an amount equivalent to about 0.05 percent by weight based on the amount of phenol.

10. The method in accordance with claim 9 in which the phenol is at a temperature above about 200 F.

11. The method in accordance with claim 10 in which the phenol is at a temperature of about 350-400 F.

12. The method in accordance with claim 11 in which the phenol is partially condensing on the metal surface.

13. The method in accordance with claim 12 in which the phenol contains a sucient amount of volatile organic acids, chloride and sulfur to accelerate the corrosion of said metal surfaces.

14. In a solvent refining process for improving the qualities of mineral lubricating oil wherein an oil is contacted in the liquid phase with phenol to produce a rafnate phase and an extract phase, which extract phase is subjected to vaporization whereby the phenol is removed in vapor form and recycled through heat exchange equipment to supply heat for said vaporization, the improvement comprising passing said phenol vapors into contact with a treating agent selectedfrom the group consisting of calcium oxide, calcium hydroxide,l calcium carbonate, barium oxide and barium hydroxide and mixtures thereof under conditions such that the treating agent reacts with deleterious corrosive materials carried by the phenol vapors and the corrosiveness of said phenol vapors is thereby mitigated.

References Cited in the file of this 4patent UNITED `STATES PATENTS 1,646,698 Koppers Oct. 25, 1927 1,873,136 Laird Aug. 23, 1932 2,246,376 Lynch June 17, 1941 2,276,089 Ragatz Mar. l0, 1942 2,420,108 Stratford et al May 6, 1947 y2,660,600 Bowman Nov. 24, 1953 2,673,174 King Mar. 23, 1954 2,701,783 Long et a1. Feb. 8, 1955 OTHER REFERENCES Dunn et al.: Oil & Gas Journal, June 9, 1952, p. 69.. 

1. IN A SOLVENT REFINING PROCESS FOR IMPROVING THE QUALITIES OF MINERAL LUBRICATING OIL WHEREIN AN OIL IS CONTACTED WITH A PHENOL SOLVENT TO PRODUCE AN OIL-RICH PHASE AND A SOLVENT-RICH PHASE WHICH ARE SUBJECTED TO HEATING CONDITIONS WHEREBY THE PHENOL SOLVENT IS REMOVED FOR RECYCLE INTO THE SYSTEM, THE IMPROVEMENT COMPRISING MAINTAINING A CONTACT MATERIAL SELECTED FROM THE GROUP CONSISTING A CALCIUM OXIDE, CALCIUM HYDROXIDE, CALCIUM CARBONATE, BARIUM OXIDE AND BARIUM HYDROXIDE AND MIXTURES THEREOF IN CONTACT WITH THE PHENOL PRIOR TO SUBJECTION TO SAID HEATIONG CONDITONS, SAID MATERIAL BEING PRESENT IN AMOUNTS UP TO THE EQUIVALENCE OF ABOUT 0.05 PERCENT BY WEIGHT BASED ON THE AMOUNT OF PHENOL AND SUFFICIENT TO PREVENT CORROSION AND PLUGGING IN THE PROCESS EQUIPMENT. 